Duration of extraction determines CO₂ and CH₄ emissions from an actively extracted peatland in eastern Quebec, Canada

Abstract

Draining and extracting peat alters the conditions that control CO2 and CH4 emissions. Carbon (C) emissions from peatlands undergoing horticultural peat extraction are not well constrained due to a lack of measurements. We determine the effect that production duration (years of extraction) has on the CO2 and CH4 emissions from an actively extracted peatland over 3 years of measurements (2018–2020). We studied five sectors identified by the year when extraction began (1987, 2007, 2010, 2013, 2016). Greater average CO2 and CH4 emissions were measured from the drainage ditches (CO2: 2.05 ± 0.12 g C m−2 d−1; CH4: 72.0 ± 18.0 mg C m−2 d−1) compared to the field surface (CO2: 0.9 ± 0.06 g C m−2 d−1; CH4: 9.2 ± 4.0 mg C m−2 d−1) regardless of sector. For peat fields, CO2 fluxes were highest in the youngest sector, which opened in 2016 (1.5 ± 0.2 g C m−2 d−1). The four older sectors all had similar mean CO2 fluxes (∼ 0.65 g C m−2 d−1) that were statistically different from the mean 2016 CO2 flux. A spatial effect on CO2 fluxes was observed solely within the 2016 sector, where CO2 emissions were highest from the centre of the peat field and declined towards the drainage ditches. These observations occur due to operators contouring surfaces to facilitate drainage. The domed shape and subsequent peat removal resulted in a difference in surface peat age hence different humification and lability. In addition, 14C dating confirmed that the peat contained within the 2016 sector was younger than peat within the 2007 sector and that peat age is younger toward the centre of the field in both sectors. Humification indices derived from mid-infrared spectrometry (MIRS) (1630/1090 cm−1) indicated that peat humification increases with increasing years of extraction. Laboratory incubation experiments showed that CO2 production potentials of surface peat samples from the 2016 sector increased toward the centre of the field and were greater than for samples taken from the 1987 and 2007 sectors. Our results indicate that peatlands under extraction are a net source of C, where emissions are high in the first few years after opening a field for extraction and then decline to about half the initial value and remain at this level for several decades, and the ditches remain a 2 to 3 times greater source than the fields but represent <3.5 % of the total area of a field.